FIG. 1 illustrates a known wireless telecommunications system wherein a public switched telephone network PSTN, a public land mobile network PLMN (e.g., AMPS, GSM, PDC) and a private wireless (e.g, cellular) network are interfaced with one another. A Gateway mobile switching center GMSC of the PLMN is coupled to the PSTN for communication therewith, and is also coupled to a home location register HLR of the PLMN. The PSTN is coupled for communication with the private network, as is the HLR of the PLMN.
The private network includes a so-called Wireless Office System WOS which is coupled to the HLR. The WOS provides a mobile extension of the wired communication systems used in office environments. Typical workspaces which can benefit from WOS technology include corporate campuses, health care facilities, manufacturing facilities, hotel chains, retail stores, etc. The WOS interfaces with HLR during call setup in the same manner as would a conventional mobile switching center (MSC).
A local exchange LE of the PSTN communicates with the WOS via a private branch exchange PBX in the private network. In some systems, the functionality of the private branch exchange PBX is included in the WOS, so the local exchange LE of the PSTN communicates directly with the WOS, as indicated diagrammatically by the broken line connection in FIG. 1. FIG. 1 shows mobile stations (mobile subscriber units) MS1 and MS2 registered and operating in the WOS. The WOS provides basic wireless telephone services in addition to the PBX services offered by private networks. The WOS does not generally provide its services to PLMN subscribers roaming in the WOS coverage area.
The communications between the HLR and the GMSC at 12, and between the HLR and the WOS at 14 can be carried out, for example, using the IS-41 protocol of the D-AMPS standard, or the MAP protocol used in GSM systems. The communications links at 16, 17 and 18 in the PSTN can be, for example, R2 or ISDN based.
Referring now also to FIG. 2, when a call to a mobile station registered in the WOS is received at 21 in the GMSC, a location request is sent at 23 from the GMSC to the HLR. The HLR then makes a routing request at 25 to the WOS to obtain therefrom a temporary routing number at 27, which the HLR relays back to the GMSC at 29.
In the setup request 21 received in the GMSC, a mobile directory number MDN (i.e., the published directory number) associated with the called mobile station is included, and the GMSC relays this mobile directory number MDN in the location request 23 to the HLR. The HLR translates the MDN to a mobile identification number MIN (each mobile station has a unique MIN conventionally coded therein), and then includes this mobile identification number MIN in the routing request 25 to the WOS. The WOS then responds just like a conventional visited MSC (VMSC), namely, it assigns a temporary local directory number TLDN to be used in routing the call. The WOS sends the TLDN to the HLR at 27 (just as a conventional VMSC would), and HLR relays the TLDN to the GMSC at 29. This sequence is well known in the art.
Then, as shown in FIG. 3, the GMSC uses the TLDN to route the call through the PSTN and access the WOS from the nearest local exchange LE. The Transit block illustrated in FIG. 1 and also designated in FIG. 3 represents a conventional routing path from GMSC through PSTN to the local exchange LE nearest the WOS. The routing path represented by the Transit block can include, for example, a plurality of conventional exchanges or switches in the PSTN.
FIG. 4 illustrates a routing handler 41 in the WOS of FIG. 1 (or in a conventional VMSC). The routing handler receives the mobile identification number MIN from HLR, and provides to HLR the temporary local directory number TLDN from a pool of TLDNs allocated to the WOS by the PSTN operator. The TLDNs are part of the public number series issued by the PSTN operator. Thus, if the WOS requires additional TLDNs due, for example, to heavy traffic conditions, such new TLDNs must disadvantageously be issued by the local PSTN operator. Also, the TLDNs are typically allocated for only a short period of time (e.g., 30 seconds) so that, if the GMSC does not use the allocated TLDN to route a particular call, (e.g., caller hangs up), the TLDN will be freed for use in other calls. This feature minimizes the size of the TLDN pool that is required, but disadvantageously requires the routing handler 41 to implement a timer/time-out function.
According to the present invention, a private network such as (or including) a WOS provides to the PLMN direct in-dialing numbers in place of temporary routing numbers, and thus advantageously requires significantly less resources to manage temporary routing numbers than does the prior art arrangement.